-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 181043
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
645 AM EDT TUE JUN 18 2013

.SYNOPSIS...
A COLD FRONT WILL APPROACH FROM THE NORTHWEST LATE TODAY...AND MOVE
SLOWLY SOUTHEAST ACROSS THE REGION TONIGHT INTO WEDNESDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 310 AM TUESDAY...

SURFACE ANALYSIS THIS MORNING REVEALED A LEESIDE TROUGH OVER THE NC
FOOTHILLS. IN ADDITION...A 1011 MB SURFACE WAVE WAS CENTERED OVER
THE MID SOUTH...ALONG A FRONTAL ZONE DRAPED FROM THE SOUTHERN PLAINS
NORTHEASTWARD THROUGH THE EASTERN TN VALLEY/CENTRAL APPALACHIANS TO
THE DELMARVA/NEW JERSEY COAST. A SEPARATE NORTHERN STREAM FRONT
ARCED FROM NEW ENGLAND SOUTHWESTWARD TO AN ELONGATED 1011 MB AREA OF
LOW PRESSURE FROM OH TO IL...THEN NORTHWESTWARD TO INTO THE UPPER
MIDWEST.

TODAY: WHILE A MOIST...WEAKLY INHIBITED...AND MARGINALLY UNSTABLE
AIRMASS OVER NC WILL NOT NEED MUCH IMPETUS TO FORCE CONVECTION...THE
COMBINATION OF SUBSIDENCE IN THE WAKE OF A LEAD MCV OVER
SOUTHEASTERN NC AT PRESENT...AND THE LOCATION OF THE SOUTHERNMOST
FRONTAL ZONE ACROSS THE TN VALLEY AND CENTRAL APPALACHIANS (IE. TO
OUR NW) SHOULD TEND TO LIMIT CONVECTIVE COVERAGE OVER CENTRAL NC
THROUGH EARLY TO MID AFTERNOON. HOWEVER...A SHORTWAVE TROUGH OVER
THE MO VALLEY THIS MORNING IS PROGGED TO LIFT ENE TO NE ALONG THE
SPINE OF THE APPALACHIAN CHAIN THIS AFTERNOON...AND THE ASSOCIATED
BRUNT OF THIS FORCING FROM THE NW NC PIEDMONT NORTHWARD THROUGH VA
SHOULD HELP FOCUS CONVECTIVE DEVELOPMENT ALONG A THE LEE TROUGH OVER
WESTERN NC/VA...WITH THIS ACTIVITY LIKELY TO SPREAD ENE ACROSS THE
WESTERN AND NORTHERN NC PIEDMONT AFTER 3 OR 4 PM. MEANWHILE...MORE
THAN A COUPLE OF THE HI-RES CAMS INDICATE AN AREA OF STORMS AND AN
ASSOCIATED MCV OVER MS/NORTHWESTERN AL THIS MORNING MAY PIVOT ENE
ACROSS THE SANDHILLS AND COASTAL PLAIN LATER THIS AFTERNOON AND
EVENING...POSSIBLY MERGING WITH THE ACTIVITY FROM THE PIEDMONT.

BOTH MARGINAL INSTABILITY OF 1000 J/KG OR LESS OWING TO WEAK LAPSE
RATES ALOFT...AS WELL AS MARGINAL EFFECTIVE BULK SHEAR IN THE 20-30
KT RANGE...STILL SUGGEST ANY SEVERE THREAT WILL BE LOW...WITH
PERHAPS A FEW STRONG PRECIPITATION-LOADED WIND GUSTS. A MORE LIKELY
SCENARIO REMAINS A THREAT OF DOWNPOURS AND LOCALIZED FLOODING...
THOUGH ANY SUCH FLOODING WILL NOT BE WIDESPREAD AND INSTEAD CONFINED
MOST LIKELY TO URBAN AREAS SINCE THE ANDREA-SOAKED SOIL HAS DRIED IN
THE PAST WEEK TO 10 DAYS...AND RESULTANT FLASH FLOOD GUIDANCE VALUES
HAVE INCREASED...INTO THE 2.5 TO 3 INCH RANGE FOR ONE HOUR FOR
EXAMPLE. HIGH TEMPERATURES TODAY ARE LIKELY TO REACH THE LOWER TO
MIDDLE 80S...WITH A FEW UPPER 80S POSSIBLE TOWARD KFAY AND KGSB.

TONIGHT: WHILE THERE MAY BE A LULL THIS EVENING AFTER THE AFTERNOON
AND EARLY EVENING CONVECTION...THE LEAD SURFACE BOUNDARY IS FORECAST
TO SETTLE SOUTHEASTWARD INTO CENTRAL NC ABOUT THE TIME THE SURFACE
WAVE OVER THE MID SOUTH TRACKS TOWARD INTO OUR REGION. THE PASSAGE
OF THE SURFACE WAVE - ONE SUPPORTED FROM ALOFT BY THE APPROACH OF A
NORTHERN STREAM SHORTWAVE TROUGH FROM THE UPPER MIDWEST THIS
MORNING - WILL ENCOURAGE RENEWED DEVELOPMENT OF AN AREA OF SHOWERS
AND ISOLATED STORMS OVER CENTRAL NC OVERNIGHT. LOWS...WITH MOSTLY
CLOUDY SKIES...IN THE MIDDLE 60S TO AROUND 70 DEGREES. TOTAL
RAINFALL AMOUNTS IN THE ONE TO TWO INCH RANGE WILL BE COMMON...
HIGHEST NORTH AND NORTHWEST...THOUGH AS WITH ANY CONVECTIVE
PRECIPITATION THERE WILL BE SOME AREAS THAT LIKELY RECEIVE
CONSIDERABLY LESS.

&&

.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
AS OF 325 AM TUESDAY...

THE NORTHERN STREAM FRONT REFERENCED IN THE NEAR TERM DISCUSSION - A
FRONT LIKELY ENHANCED BY NE MARITIME FLOW FROM CHESAPEAKE BAY
REGION - WILL NOT DRIFT SOUTHWARD THROUGH CENTRAL NC UNTIL THE
AFTERNOON WEDNESDAY. HOWEVER...THE MAIN CONVERGENCE AXIS WITH THE
LEAD FRONT TRAILING THE SURFACE WAVE TRACKING FROM THE MID-SOUTH TO
NC COAST WILL HAVE DRIFTED INTO SOUTHERN OR SOUTHEASTERN NC BY WED
MORNING. AS SUCH...HAVE TRENDED POPS DOWNWARD INTO THE CHANCE
RANGE...RANGING FROM AROUND 30 PERCENT NW...TO 50 PERCENT IN CLOSEST
PROXIMITY TO THE LEAD FRONT/CONVERGENCE AXIS AND WHERE BOUNDARY
LAYER MOISTURE IN THE UPPER 60S IS LIKELY TO LINGER...OVER THE SE.
HIGHS...WITH A MIX OF SUN AND CLOUDS...AGAIN IN THE LOWER TO MIDDLE
80S. CLEARING AND COOLER WITH LOWS IN THE LOWER TO MIDDLE 60S
OVERNIGHT...THOUGH A FEW PATCHES OF STRATUS IN NE LOW LEVEL FLOW
WILL BE POSSIBLE LATE.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
AS OF 315 AM TUESDAY...

THURSDAY THROUGH FRIDAY NIGHT...HIGH PRESSURE BUILDS ACROSS SOUTHERN
NEW ENGLAND SHORE...EXTENDING DOWN THE MID ATLANTIC COAST WITH DRY
NORTHEAST TO EAST FLOW. THE PLEASANT ENSUING COOL DAMMING SCENARIO
WILL LINGER INTO THE WEEKEND...WITH THICKNESSES INDICATIVE OF TEMPS
A GOOD CATEGORY BELOW NORMAL...LOW-MID 80S. WILL MAKE SOME GRID
ADJUSTMENTS ON THURSDAY AND FRIDAY TO FAVOR COOLER TEMPS IN THE
NORTHEAST WHERE MARITIME FLOW WILL BE STRONGEST/COOLEST. MINS WILL
BE GENERALLY LOW AND MID 60S.

SATURDAY THROUGH MONDAY...THE COOL SURFACE HIGH WILL WEAKEN AND
DRIFT EAST WITH A GRADUAL RETURN OF MORE SOUTHERLY FLOW BY LATE
WEEKEND. MEANWHILE...UPPER RIDGING WILL BUILD EAST OUT OF THE
MIDWEST INTO THE EASTERN CONUS SATURDAY THROUGH MONDAY. SOUTHERLY
FLOW WILL RESULT IN INCREASING HUMIDITY SUNDAY INTO MONDAY. WITH THE
CAPPING MID LEVEL RIDGE OVERHEAD...CONVECTION WILL BE ISOLATED
OUTSIDE OF PERHAPS SOME DIFFERENTIAL HEATING ON THE EASTERN SLOPES
AND POTENTIAL FOR SOME SEA BREEZE CONVECTION TO MIGRATE INLAND INTO
THE COASTAL PLAIN. AT THIS POINT...THE CHANCES ARE TOO SMALL TO
MENTION IN THE FORECAST. THE AIRMASS WILL GRADUALLY WARM UP WITH THE
SOUTHERLY FLOW AND PERSISTENCE OF THE UPPER RIDGE INTO MONDAY...
HIGHS WILL WARM FROM THE MID 80S SATURDAY TO THE UPPER 80S...PERHAPS
LOWER 90S ON MONDAY. MINS WILL BE IN THE 60S.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --
AS OF 645 AM TUESDAY...

CEILINGS WILL BE HIGHLY VARIABLE IN THE UNSETTLED AIRMASS OVER THE
AREA TODAY. PATCHY LINGERING IFR CEILINGS THIS MORNING WILL LIFT TO
MVFR BY MID MORNING AND SHOULD REMAIN MOSTLY VFR/MVFR OUTSIDE OF
PRECIPITATION.

A COLD FRONT STALLED NORTH OF THE AREA WILL BE MOVING SOUTHEAST AND
ACROSS THE AREA LATE TODAY. FORCING WILL BE RATHER WEAK AHEAD OF THE
FRONT...BUT THE AIRMASS OVER THE AREA IS MOIST AND WARM...THUS PRONE
FOR ALMOST RANDOM SCATTERED SHOWER AND ISOLATED THUNDER DEVELOPMENT
THIS MORNING. THE FRONT...ACCOMPANIED BY A MORE WIDESPREAD AREA OF
SHOWERS AND THUNDERSTORMS...WILL BE MOVING INTO THE NORTHWEST DURING
PRIME DIURNAL TIMING...AROUND 18Z...WITH ACTIVITY PROGRESSING
SOUTHEAST. STORMS WILL BE ACCOMPANIED BY WIND GUSTS TO 25 KNOTS.
CONFIDENCE IN THE SPEED OF FRONTAL PROGRESSION IS NOT HIGH...BUT
EXPECT ACTIVITY TO BE LARGELY OUT OF THE AREA BY 19/06Z. SOUTH TO
SOUTHWEST WINDS WILL BE DOMINANT TODAY...SWINGING MORE WESTERLY
AFTER THE FRONT MOVES THROUGH THIS EVENING...THEN NORTHERLY
BY THE END OF THE TAF PERIOD.

VFR CONDITIONS ARE GENERALLY EXPECTED FROM WEDNESDAY ONWARD...
OUTSIDE OF POSSIBLY SOME EARLY MORNING STRATUS AND OR FOG DURING THE
PRE-DAWN HOURS OF EACH MORNING.
-- End Changed Discussion --

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

SYNOPSIS...MLM
NEAR TERM...MWS
SHORT TERM...MWS
LONG TERM...MLM
AVIATION...MLM